One in five young Australians are dealing with mental illness, but more than 60% felt uncomfortable seeking professional help, according to a new report by Mission Australia and the Black Dog Institute.

The study of 15- to 19-year-olds across the country found 21% of the 15,000 surveyed were battling a probable mental illness. The rate among females in that age group was much higher than among young men – 26% compared with 14%.

Aboriginal and Torres Strait Islanders and young people with a disability were also more likely to be experiencing mental illness.

But less than 40% felt comfortable seeking information, advice or support from community agencies, online counselling or telephone hotlines.

"The confronting findings in this report illustrate the significant challenges many of our young people are facing when it comes to psychological distress and mental health issues," Mission Australia’s CEO, Catherine Yeomans, said on Wednesday.

"We know that many of our youth are struggling with complex issues, and it's impacting on their ability to transition with confidence into adulthood."

Yeomans said early intervention and support is critical to help those vulnerable.

The Youth Mental Health Report was based on a survey that asked respondents to answer questions about their experiences of anxiety and depressive symptoms over a period of four weeks.

• Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14 or Suicide Call Back Service 1300 659 467.